Positional data utilizing inter-vehicle communication method and traveling control apparatus

ABSTRACT

Predicted future positions are calculated (S 11 ) and arranged into packets (S 12 ) to be transmitted using a communication pattern (for example, a PN series) based on a time and a position of each packet (S 13 ). Another vehicle calculates its predicted position (S 21 ) and generates a communication pattern based on a result of calculation (S 22 ) so that the generated communication pattern is utilized for reception (S 23 ). Consequently, data associated with a future position of its own can be selected for enabling reception. An existence probability is calculated, and the state of another vehicle can be accurately understood from the communication of the calculated existence probability, thereby effectively reducing chance of collision.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for performingcommunication with another vehicle having similar positional data basedon broadcast positional data. The present invention also relates to anavoidance operation when it is recognized that there is a possibility ofa collision with another vehicle.

2. Description of the Related Art

Systems for collecting a variety of information using a vehicle mountedcommunication apparatus, systems for collecting destination informationof each vehicle to be utilized in traffic control, and a variety ofother systems have all been proposed.

Inter-vehicle communication has been proposed where a moving or stoppingvehicle will notify another vehicle of its actions or of informationobtained in communication between the vehicles.

With such inter-vehicle communication, along with useful data,unnecessary information is often transmitted and received. For example,even if information of future traveling/stopping of a vehicle which hasbrushed is received, it usually has no meaning. Therefore, ininter-vehicle communication, there are many requests to effectivelyselect useful data from all received data.

Furthermore, Japanese patent laid-open publication No. Hei 7-333317discloses an apparatus that transmits/receives position informationbetween movable bodies and raises an alarm when both movable bodies areapproaching a predetermined distance.

Moreover, there has been proposed a system for averting vehiclecollision by performing communication between vehicles (inter-vehiclecommunication) and measuring the distance between the vehicles. The “SSboomerang system” is one such system. In the “SS boomerang system,” anelectromagnetic wave is broadcast, and a response is returned byvehicles which receive that signal. The response time is measured tocalculate the distance between the vehicles to allow the possibility ofcollision to be reduced.

However, with inter-vehicle communication for measuring the distancebetween vehicles based on the response time of the transmitted electricwave, accurate motion information of another vehicle other than thedistance between the vehicles is difficult to obtain.

In addition, it is not negligible that the avoidance operation carriedout by the both vehicles that have possibility of a crash is notnecessarily appropriate.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an inter-vehiclecommunication apparatus capable of receiving only necessary informationin a vehicle by including positional data in a communication protocol.

It is another object of the present invention to provide a vehiculartraveling control apparatus for executing control to avert a collisionwith another vehicle by obtaining accurate motion information of theother vehicle through inter-vehicle communication.

According to one aspect of the present invention, a communicationpattern is determined based on the position of the user's vehicle.Therefore, transmission data is received in the vehicle that hasreceived data in accordance with the communication pattern at thatposition. Thus, a signal required for reception can be automaticallyselected.

For example present position and projected positions at two secondslater, four seconds later, . . . , n seconds later are represented inthe form of time data and positional data, and the communication patternis determined based on these data. As such a communication pattern, thePN series for the spread spectrum or the frequency hopping pattern maybe adopted. For example, when the PN series is determined based on thetime and position and then transmitted, the inverse spread is performedonly in a vehicle using the same PN series to receive signals. In otherwords, on the receiving side, only signals that coincide with the futuretime and position of the user's vehicle.

Further, it may be preferable to determine a search range for thecommunication pattern based on a range related to traveling of theuser's vehicle, whereby this vehicle can communicate with anothervehicle in that range.

When it is determined that there is a possibility of collision, it maybe preferable to select a communication pattern for emergency. Thisenables identification of the emergency communication from any othercommunication.

Furthermore, it may be preferable to narrow the search range whenanother vehicle approaches. This can narrow the search range to selectonly a specific emergency communication to be performed.

Moreover, according to another aspect of the present invention,existence probability data can be calculated based on the positionaldata of the user's vehicle and position error data. The accuracy of thisexistence probability data can be greatly increased by utilizing theposition error data.

Use of the existence probability data can allow precise motioninformation of another vehicle to be obtained to assist carrying out ofaccurate avoidance control.

Additionally, according to yet another aspect of the present invention,relative position data of the user's vehicle and another vehicleobtained from the inter-vehicle communication is used to generate theexistence probability data of the user's vehicle in order to executeavoidance control.

In addition, according to a further aspect of the present invention, theuser's vehicle and another vehicle do not perform the uniform avoidanceoperation even when there is a possibility of a collision. Rather, theoperation for averting collision is executed based on the priority ofthe user's vehicle and of the other vehicle. This can prevent affectingthe travel of the other vehicle or the traffic flow while stilleffectively avoiding collision.

Furthermore, when the user's vehicle travels on a privileged road, it ispreferable to suppress the avoidance operation of that vehicle and givepriority of the avoidance operation to another vehicle. This enablesavoidance of a collision without adversely affecting any other vehiclerunning on the privileged road.

Moreover, in regard to priority, the difficulty of the avoidanceoperation and the influence on other traffic also depends on the speedsat which the vehicles are travelling. For example, when the speed of theuser's vehicle is lower than that of another vehicle, it is relativelyeasy to execute an avoidance operation through the user's vehicle.Accordingly, determining the priority based on the vehicle speed caneffectively avoid collision.

In addition, avoiding collision with a first vehicle is pointless ifthis action increase the possibility of a collision with a secondvehicle. Taking into account the possibility of collision with thesecond vehicle when the user's vehicle is performing an avoidanceoperation, it is preferable to carry out the avoidance operation whenthere is no possibility of collision with an additional vehicle. Thiscan avoid collisions and help maintain smooth traffic flow.

Additionally, in the inter-vehicle communication, transmission/receptioninformation for determining which vehicle should move to avert acollision can assist in effectively avoiding collision.

Further, even if the user's vehicle takes priority, it is preferable todetermine that avoidance operation should not be carried out uponreceiving data representative of execution of the avoidance operationfrom another vehicle. For example, the user's vehicle executes theavoidance operation in principle, even when it takes priority, unlessdata indicating that another vehicle is performing an avoidanceoperation is received from that vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the structure of an apparatus according to thepresent invention;

FIG. 2 is a view showing the structure of the data communication section(transmitting side) of the apparatus shown in FIG. 1;

FIG. 3 is a view showing the structure of the data communication section(receiving side) of the apparatus shown in FIG. 1;

FIGS. 4A and 4B are views showing the content of communication of theapparatus shown in FIG. 1;

FIG. 5 is a block diagram showing an example of the structure accordingto a second embodiment of the present invention;

FIG. 6 is a view illustrating inter-vehicle communication according to asecond embodiment of the present invention;

FIG. 7 is a view explaining a direction from which an electronic signalis transmitted;

FIG. 8 is a flowchart showing the operation for averting collision;

FIG. 9 is a flowchart showing the response operation according to asecond embodiment of the present invention;

FIG. 10 is a flowchart showing the control of a transmitting/receivingseries according to a second embodiment of the present invention;

FIG. 11 shows allocation of the PN series according to a secondembodiment of the present invention;

FIG. 12 shows allocation of positional data according to a secondembodiment of the present invention;

FIG. 13 shows a circuit for generating the PN series according to asecond embodiment of the present invention;

FIGS. 14(a), 14(b) and 14(c) are explanatory drawings showing control ofthe PN series; according to a second embodiment of the presentinvention;

FIG. 15 is a block diagram showing the system structure of a vehiclecrash avoidance control apparatus according to a third embodiment of thepresent invention;

FIG. 16 is a flowchart showing a former part of the vehicle crashavoidance control processing according to the third embodiment of thepresent invention;

FIG. 17 is a flowchart showing a latter part of the vehicle crashavoidance control processing according to the third embodiment of thepresent invention;

FIG. 18 is a graph showing position coordinates of four corners of avehicle;

FIG. 19 is a graph showing an existence probability distribution in aspace-time of the user's vehicle from present to a few seconds later;

FIG. 20 is a graph showing position coordinates of the user's vehicleand another vehicle from present to a few seconds later;

FIG. 21 is a flowchart showing determination of an avoidance priorityaccording to the third embodiment;

FIG. 22 is a block diagram showing the system structure of a vehiclecrash avoidance control apparatus according to a fourth embodiment ofthe present invention;

FIG. 23 is a flowchart showing a former part of the vehicle crashavoidance control processing according to the fourth embodiment of thepresent invention;

FIG. 24 is a view showing the position of the vehicle relative to thatof another vehicle;

FIG. 25 is a block diagram of the structure according to a fifthembodiment of the present invention;

FIG. 26 is a flowchart of the entire processing (part 1) according tothe fifth embodiment;

FIG. 27 is a flowchart of the entire processing (part 2) according tothe fifth embodiment;

FIG. 28 is a view showing the transmission structure of a datacommunication section according to the fifth embodiment;

FIG. 29 is a view showing the reception structure of the datacommunication section according to the fifth embodiment;

FIG. 30 is a detailed flowchart of the optimum vehicle avoidance controlaccording to the fifth embodiment;

FIG. 31 is a detailed flowchart of the traffic priority check accordingto the fifth embodiment;

FIG. 32 is a detailed flowchart of the avoidance control according tothe fifth embodiment;

FIG. 33 is an explanatory drawing of predicted trajectories in aspace-time of one's vehicle and another vehicle according to the fifthembodiment; and

FIG. 34 is an explanatory drawing showing a positional relationshipbetween the vehicle and another vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings.

First Embodiment

Structure

FIG. 1 is a block diagram showing the system structure according to afirst embodiment of the present invention. A detection signal from asensor 10 such as a GPS, a steering sensor, or a clock is supplied to anECU 12. Then, a position of the vehicle, time, motion of the vehicle andother information are determined using the supplied detection signal.For example, a prediction value such as a future time and a position isobtained. This data is supplied to a data communication section 14 wherea carrier is modulated. Additionally, in this communication section 14,a communication pattern such as a PN series in the spread spectrumcommunication or a frequency hopping pattern is determined based on thepresent and future positional data of the user's vehicle, and atransmission signal based on this communication pattern is formed to betransmitted to another vehicle via an antenna 16.

Further, the data from another vehicle received via the antenna 16 isdemodulated in accordance with the communication pattern based on thepresent position and the future position of the user's vehicle in thedata communication section 14, and a modulation signal is retrieved sothat its content is recognized in the ECU 12.

An actuator 18 for brake, steering, or the like is connected to the ECU12, and the actuator 18 is driven to operate the brake or steering whenit is determined that operation of such a member is necessary as aresult of recognition by the ECU 12.

FIG. 2 illustrates the structure of a transmitting side of the datacommunication section 14. In this example, the PN series based on theposition is generated as a communication pattern, and this is used toperform direct spread. The transmission data is mixed with the carrierin a primary modulating section 20, and the carrier is then modulated(primary modulation) with the transmission data. The transmission datamay, for example, be positional data from the present to a point infuture as estimated at predetermined intervals. Further, thistransmission data may, for example, be digital pulse data. A numericalsequence which is generated based on positional data and other data asdescribed below is fed into a PN series generator 22 where the PN seriesbased on the number sequence is generated. This PN series is input to amultiplier 24 to be mixed with a signal subjected to primary modulation,and thereafter a desired spread spectrum is performed. Then, in a BPF(band-pass filter), a signal having a predetermined frequency band isselected to be transmitted from the antenna 16.

Next, FIG. 3 shows the structure of a receiving side of the datacommunication section 14. A reception signal received via the antenna 16is selected to a predetermined band in the BPF 30 and thereaftersupplied to the multiplier 32. To the multiplier 32 is supplied the PNseries from the PN series generator 34, and the inverse spread spectrumis performed with this PN series. It is to be noted that a numbersequence generated based on the later-described positional data of theuser's vehicle is supplied to the PN series generator 34, and the PNseries is generated based on this number sequence. Therefore, the signalsubjected to the inverse spread spectrum in the multiplier 32 issupplied to the demodulator 36 where the data can be obtained.

Generation of Communication Pattern

As described above, in this embodiment, although the spread spectrum isperformed in accordance with the PN series, generation of the PN serieswill now be described.

The PN series is generated based on time, positional data, and otherinformation. For example, when the future position based on the presenttime is as shown in Table 1:

TABLE 1 Time Existence (seconds later) Position (coordinate) Probability1.01 (1012.6, 104.6, 15.2) (1.0)  2.20 (1010.3, 105.2, 15.2) (0.95) 3.35(1008.3, 107.2, 15.2) (0.88)

In this case, the time and the positional data are rounded off in aproper unit to be combined so that a series of a number sequence isgenerated. The processing for rounding off in a proper unit is performedby setting a value to which the LSB of that number corresponds. Forexample, when the LSB corresponds to 1 km, it can be said that they arerounded to 1 km. Then, that sequence of numbers is subjected to apredetermined encoding processing so that the number sequence israndomized, thereby obtaining a sequence of numbers (random numbers)which is a base of the PN series. For example, an encoded numbersequence such as shown in Table 2 is obtained:

TABLE 2 Rounding off → Combining Encoding 1.0, 1013, 0105, 15 →101013010515 → 730184621803869 2.0, 1010, 0105, 15 → 201010010515 →846247575839570 3.5, 1008, 0107, 15 → 351008010715 → 846120973956829

The PN series is created based on the thus-obtained number sequence, andthe obtained result is used to perform spread spectrum communication. Itis to be noted that the information to be actually transmitted mayinclude the accurate time, positional information, existence probabilityat that position, and other information, and this is turned into pulsesto be carried as digital communication. It should be noted that anyother useful or helpful information may be likewise included.

On the other hand, on the receiving side, although a sequence of numbersis generated based on the rounded time and positional data of the user'svehicle as similar to the transmitting side, a number sequence to whichthe proximate data is added is generated if necessary. For example, aplurality of sequences of numbers such as shown in Table 3 are generatedand these are used to perform the inverse spectrum spreading:

TABLE 3 Time, Position →Adding Proximate Data → Combining → Encoding1.0, 1013, 0105,15 →1.0, 1013, 0105, 15 → 101013010515 → 730184621803869→1.0, 1014, 0105, 15 → 101014010515 → 530144621893867 →1.5, 1013, 0105,15 → 151013010515 → 730884621893865 →1.5, 1013, 0106, 15 → 151013010615→ 930984621703863 2.0, 1010, 0105, 15 →2.0, 1010, 0105, 15 →201010010515 → 846247575839570 →2.0, 1009, 0105, 15 → 201009010515 →746368986539547 →2.5, 1010, 0105, 15 → 251010010515 → 3462475758395783.5, 1008, 0107, 15 →3.5, 1008, 0107, 15 → 351008010715 →846120973956829 →3.5, 1007, 0108, 15 → 351007010815 → 846120973957820→4.0, 1009, 0107, 15 → 401009010715 → 746128973956828

In this manner, the transmitting side estimates the position to whichthe user's vehicle will move in the future over time and uses the PNseries based on this estimation to create the spread spectrum.Similarly, on the receiving side, the inverse spread spectrum is createdin accordance with the PN code based on the position to which the user'svehicle will move in the future (including the proximity) and the time.Therefore, the data obtained by the inverse spread spectrum correspondsto the information about a vehicle that runs in the vicinity if theuser's vehicle travels in the future.

When the proximate data is processed in the encoding in such a mannerthat the number sequence is also turned to a proximate number sequence,addition of the data can be omitted. That is, if the sequence of numberis the proximate counterpart, the PN series is likewise turned to theproximate PN series to be received as leakage electromagnetic radiation.

The thus-generated number sequence is received as random numbers fordetermining the PN series. In this way, a plurality of PN series signalsmay be received by one receiver in time series, or the respective PNseries signals may be received by a plurality of receivers in parallel.Further, combining the above-described sequences of numbers can generateand simultaneously receive the PN series for receiving all the relatedsignals. In such a case, the data is then separated based on each PNseries.

In this fashion, the PN series is generated based on the current andfuture positions, and each vehicle transmits the information obtained byperforming spectrum spreading using the PN series. On the other hand, asto reception, the inverse spread spectrum utilizing the PN seriesgenerated based on the current and future positions of the user'svehicle is created. Accordingly, the information to be received isrestricted to that having the matched PN series, i.e., the current andfuture positions overlapping on the positions of the user's vehicle. Itis to be noted that setting a range that the positional data indicatesto a wide system also enlarges the receivable range. In this manner,since the communication protocol itself includes the positionalinformation, just the information concerning the user's vehicle need beselected to enable reception.

Although the above example is one wherein the PN series is used as thespread spectrum, a similar operation is possible using frequencyhopping. That is, on the transmitting side, a pattern for a hoppingfrequency is created based on an encoded number sequence (randomnumbers) generated as shown in Table 2, and the hopping frequency isused to modulate the carrier. In other words, the frequency is subjectedto hopping in accordance with the PN series generated in the PN seriesgenerator shown in FIG. 2, and a signal obtained by frequency hopping ismixed with a primary modulation signal to carry out the spread spectrummodulation, thereby transmitting the data. On the other hand, on thereceiving side, the generated hopping frequency is used based on anencoded number sequence (random numbers) produced as shown in Table 3 tocreate the inverse spread spectrum, thereby demodulation the data.

Moreover, in the above example, different sequences of numbers aregenerated from the time and position values and the spread spectrum iscreated from these on the transmitting side. Therefore, the data to besent is divided using different sequences of numbers and thereaftertransmitted. However, the data which is the content of transmission maybe subjected to the spread spectrum as a single data packet by using asingle sequence of numbers.

In such a case, a number sequence used for the spread spectrum (PNseries, hopping frequency) may be created based on only the currentposition coordinate of the user's vehicle. Here, the LSB of the positioncoordinate to be rounded off is set large. By doing so, a transmissionsignal can be received in a vehicle in a relatively-large rangesurrounding the position of the user's vehicle.

Additionally, setting the large LSB can increase the probability that aplurality of vehicles exist at the same position. Thus, in order toeliminate interference of signals transmitted from a plurality ofvehicles, it is preferable to add a sequence of numbers corresponding toa vehicle ID to a sequence of numbers of the position information todetermine a sequence of numbers for the spread spectrum. For example, asshown in Table 4, the vehicle ID is added before the positional data:

TABLE 4 Vehicle ID, Position(Coordinate) →Combining →Encoding 0323,(1012.0, 1411.0, 15.0) →03231012141115 →846120973956829

Spread spectrum modulation is executed using the thus obtained sequenceof numbers. On the other hand, the vehicle ID on the transmitting sideis unknown on the receiving side. Therefore, the PN series having allthe combinations is generated with respect to the part corresponding tothe vehicle ID, and information from a plurality of vehicles areindividually received. According to this method, there is no problem ininterference of communication from a plurality of vehicles having thedata in which the PN series other than the vehicle ID is the same (timesand positions are identical).

Further, the vehicle ID may be inserted into the transmission data inplace of the PN series. As a result, the vehicle ID can be recognizedafter reception and the information for each vehicle can be individuallyobtained.

In this manner, the data representative of the traveling state ofanother vehicle concerning the future running of the user's vehicle canbe automatically obtained. Therefore, various kinds of processing can beperformed based on this data. Particularly, in the present embodiment,special processing for extracting the data relating to the user'svehicle need not be carried out, and there is additional merit in thatthe data concerning the user's vehicle can be automatically selected.

Probability of Scrape, Calculation of Impact Shock

The relationship between the time and the position of a vehicle in thefuture can be estimated based on the current traveling status. Forexample, after input, the current GPS position coordinate, a turningspeed(yaw rate), a steering angle, a vehicle speed, an acceleration, adriving torque estimate, a road surfaceμ estimate, a road surface cant,a slope estimate, an estimated weight of vehicle and others, theposition coordinates of four corners of a vehicle in a space-time fromthe present to a few seconds later can be calculated.

For estimation, any of the following example methods may be employed:

(i) a sequential simulation is carried out in accordance with atwo-wheeled or four-wheeled vehicle model to specify a spatiotemporalposition; and

(ii) the above inputs, the spatiotemporal coordinate from the start timeto a few seconds later and a probability distribution pattern arepreviously calculated a number of times to sequentially specify aspatiotemporal position from the input data during traveling by aneutral network, etc.

In this way, the future position coordinate of the vehicle can beestimated, and hence the user's vehicle can inform another vehicle ofits future motion by transmitting the vehicle position from eachvehicle.

Thus, when receiving a spatiotemporal position of another vehicle,comparing the spatiotemporal position of each vehicle with that of theuser's vehicle can obtain the collision probability. That is, if thespatiotemporal positions of the user's vehicle and another vehicleoverlap one on another at parts where each existence probability is100%, the probability of scrape is 100%. Further, if they overlap one onanother at a part where the existence probability is 1 to 100%, when aproduct of the probabilities of the overlapped parts is a maximum value,that value is the existence probability.

Since the velocity vector of both the user's and that of the other partyare known, a magnitude of impact shock is a value which is proportionateto the square of an absolute value of the obtained relative velocity ofthe both vehicles at the time of occurrence of the first scrapeprobability.

In this manner, the probability of scrape and the magnitude of impactshock can be estimated. Thus, the ECU controls the actuator to operatethe brake and/or the steering, thereby executing the avoidanceoperation.

Further, during automatic driving, distance control may be carried outwherein a target course for assuring a sufficient distance between theuser's vehicle and another vehicle for averting collision or the like iscalculated, and the vehicle is guided to this course.

Furthermore, during route searching, a number of vehicles traveling inthe same space-time at an intersection through which those vehicles willpass is determined based on the received data, and recalculation of theroute and other data is executed.

Here, FIG. 4A shows a flowchart of the transmission processing by theuser's vehicle, while FIG. 4B shows the processing in another vehiclethat receives the transmitted data.

The user's vehicle obtains its position derived by GPS or other meansand predicts its future from detection values from various sensors tocalculate a predicted position in the future with the time as a function(S11). Then, the data representative of positions of the user's vehicleat the present time, two seconds later, . . . , n seconds later arearranged into individual data packets (packet 1 (the present, theposition coordinate at the present time), packet 2 (two seconds later,the coordinate of two seconds later), . . . ) (S12). Each packet istransmitted in accordance with the communication pattern (the PN seriesor the frequency hopping) associated with its time and coordinate (S13).

On the other hand, in another vehicle, a predicted position in thefuture is obtained with the time as a function (S21) and thecommunication pattern associated with the obtained position and the timedata is calculated as similar to the user's vehicle (S22). The datacorresponding to this communication pattern is received and demodulated(S23).

Recalculation of route (S24), crash avoidance operation (S25),inter-vehicle control (S26), and other processes are carried out basedon the obtained data.

Second Embodiment

A system which can change the PN series or the transmission series ofthe frequency hopping and a range of reception search in accordance withconditions such as a vehicle position grasping situation, a state ofapproach of another vehicle, a vehicle state and which can rapidlyobtain information as needed is described in the second preferredembodiment of the present invention.

In this system, on a user's vehicle is mounted an inter-vehiclecommunication apparatus as shown in FIG. 5. A detection signal from asensor 10 is supplied to an ECU 12. The ECU 12 grasps the state of theuser's vehicle such as current or future positions of the user'svehicle. The ECU 12 feeds such positional data to a PN generator 40. ThePN generator 40 produces a PN series based on the positional data asdescribed above and supplies it to a multiplier 42. To the multiplier 42is supplied a predetermined carrier wave from a carrier wave generatingsection 44, and the spread spectrum is carried out by multiplying thecarrier wave by the PN series. The obtained result is supplied to anantenna 16 via a transmitter 46 to be transmitted from the antenna 16.

An actuator 18 for brake or steering is further connected to the ECU 12and, when it is determined by this ECU 12 that operation of the brake orthe steering is necessary, the actuator 18 is driven to operate thebrake or steering accordingly.

Meanwhile, an electric wave received by the antenna 16 is subjected toreception processing in a receiver 48, and the obtained reception signalis fed to a response circuit 50. This response circuit 50 does notchange the PN code of the reception signal but rather frequency-convertsthe reception signal to produce a response signal as a signal having acarrier wave different from that of the received frequency. The responsecircuit 50 also supplies a response signal which is delayed by apredetermined delay time to the antenna 16 through the transmitter 46.Therefore, the PN series by which the reception signal is transmitted isdelayed by a predetermined time and the response signal is returned withthe carrier wave having a different frequency.

A signal from the multiplier 42 is added to the response signal so thatinformation of the user's vehicle is included in the result signal.Although the PN series to be multiplied by the multiplier 42 may be thesame PN series for reception, both can readily be separated from eachother because the frequencies of the carrier waves differ.

The reception signal from the receiver 48 is also supplied to asynchronism detecting section 52. This synchronism detecting section 52detects a phase of the PN series from the returned carrier wave. To thesynchronism detecting section 52 is supplied the PN series from the PNgenerator 40 so that the detected PN series (received PN series) iscompared with the transmitted PN series to detect a phase difference ofthese two types of the PN series. It may be preferable that thiscounting be carried out by a counter using a carrier wave as a clock assuch enables highly accurate detection of phase differences.

A signal indicative of this phase difference is sent to adistance/direction measuring section 54. As described above, the phasedifference of the PN series is produced because the PN series istransmitted and returned to or from another vehicle, and corresponds tothe time required for the PN series to be transmitted to another vehicleand back and the time which is a sum of the delay time in the responsecircuit 50 of another vehicle. The time in which the PN series istransmitted and returned is made apparent by setting the delay time inthe response circuit 50 in each vehicle to a fixed value, and hence thedistance to another vehicle can be detected based on the obtained time.

The detection of the distance/direction in the distance/directionmeasuring section 54 is described in the following using an examplewherein another vehicle is also equipped with a similar apparatus sothat a signal is returned from the response circuit 50 in that othervehicle. In such a case, the delay time is known in advance. Therefore,when subtracting this delay time and evaluating the phase difference ofthe PN series, the phase difference corresponds to a propagation time ina route where the electric wave is transmitted from the user's vehicleto another vehicle and the user's vehicle in order, as shown in FIG. 6.Accordingly, when the time corresponding to this phase difference isdivided by the velocity of light and then by ½, the distance to theother vehicle can be determined.

Further, in this embodiment, three antennas 16 a, 16 b and 16 c areprovided as the antenna 16. All three antennas 16 a, 16 b and 16 c areutilized to perform reception. Here, these three antennas 16 a, 16 b and16 c are placed so as to form a regular triangle (each inner angle is 60degrees) as shown in FIG. 7, and the antenna 16 a is set on the frontside of a vehicle and a line connecting the antennas 16 b and 16 c ispositioned in the width direction of the vehicle. If a carrier wave ofthe electric wave from another vehicle arrives along a direction θ withrespect to a longitudinal direction of a vehicle, the carrier wavesreceived by the antennas 16 b and 16 c have phase differences(distances) a and b associated with θ with respect to the carrier wavereceived by the antenna 16 a. By detecting distances a and b from thephase differences, θ can be obtained using the following expression:

θ=a tan[−1.5(a−b)/(3a ³−3ab+3b ³)^(½)/{0.866(a+b)/(3a ³−3ab+3b ³)^(½}])

It is to be noted that a and b are the phase differences of the carrierwaves received by the antennas 16 b and 16 c with respect to the phaseof the carrier wave received by the antenna 16 a.

Additionally, an angle of elevation φ can be calculated using thefollowing formula:

φ=a cos(2/3(3a ²−3ab+3b ²)^(½) L)

where L is a distance between the respective antennas.

It is to be noted that the carrier wave from the carrier wave generatingsection 44 is modulated using information representative of the user'svehicle in the modulating section. Then, the receiving vehicle canobtain the information transmitted using the carrier wave.

Meanwhile, the reception signal obtained by the receiver 48 is fed fromthe synchronism detecting section 52 to the demodulating section. Inthis demodulating section, the PN series synchronized with thecounterpart of the reception signal obtained in the synchronismdetecting section 52 is multiplied to create an inverse spread spectrum.The result is then demodulated to obtain the information transmittedfrom another vehicle.

The operation of the ECU 12 in one vehicle is e described in thefollowing with reference to FIG. 8.

First, the information representative of the traveling condition of theuser's vehicle, such as the accelerator position, the angle of thesteering wheel, yaw rate, acceleration, positional information, andother data is retrieved from a detection result of the sensor 10 (S31).Subsequently, a vehicular motion of the user's vehicle is calculatedfrom the retrieved information representative of the traveling condition(S32). For example, a trajectory of the position coordinates of thevehicle from the present time to a projected point in the future isoperated and calculated utilizing a neutral network. Atransmission/reception series determining routine is implemented (S33)to determine the PN series in transmission and reception. S33 isdescribed below.

The motion data of the user's vehicle obtained from calculation of amotion of the user's vehicle is transmitted in accordance with apredetermined transmission procedure (S34). Then, a judgment is made asto whether an electric wave returned from another vehicle is obtainedwithin a predetermined time (S35). When the judgment at S35 is NO, anarithmetic operation of a possibility of collision or the like isunnecessary, and the control returns to S31.

On the other hand, if the electric wave returned from another vehicle isreceived, a distance and a direction with respect to that other vehicleis calculated from phases of the transmitted wave and the returned waveas described above (S36). The probability of a collision is thencalculated from the vehicular motion data, the distance and thedirection of the user's vehicle and the other vehicle (S37). Thiscalculation is executed based on a prediction calculation of futurepositions of both of the vehicles.

Thereafter, a judgment is made as to whether the probability of acollision is high based on a result of calculation in S37 (S38). If theprobability is judged to be low, the avoidance processing or the like isnot necessary, and the control returns to S31. On the other hand, whenthe judgment at S38 is YES, the actuator 18 is controlled to carry outthe avoidance control by which the brake or the steering is operated inorder to avert a collision (S39).

In this manner, the probability of a collision can be obtained byacquiring the motion data of another vehicle in the inter-vehiclecommunication with another vehicle and comparing it with the motion dataof the user's vehicle. In particular, since the transmitted signal whichwas subjected to the spread spectrum modulation is obtained by furtherbeing subjected to the inverse spread based on the positional data, theinter-vehicle communication is restricted to the communication betweenvehicles relating to time or position. Consequently, communication canbe accomplished efficiently.

FIG. 9 illustrates the processing when receiving the transmittedelectric wave from another vehicle. First, a judgment is made as towhether the transmitted electric wave from another vehicle is received(S41) and, if the judgment is NO, this judgment is repeated. If a YESjudgment is obtained at S41, the motion data of the user's vehicle isbroadcast (S42). This return operation is carried out utilizing theresponse circuit 50.

FIG. 10 shows the operation of the transmission/reception seriesdetermining routine in S33. At first, in the ordinary state, the PNseries for each of transmission and reception is determined based on theposition of the user's vehicle (S51).

For example, it is assumed that the user's vehicle is represented as avehicle A and it is determined that the vehicle A exists at such aposition as shown in FIG. 11 using a GPS apparatus or the like. In sucha case, the PN series is determined in the A vehicle as shown in FIG. 11based on the detected positional data. In other words, the travelingarea in a range in which an electric wave from the vehicle A can bereceived is divided as shown in the drawing. The PN series in apredetermined range is allocated in each area.

Two position vectors are allocated to each area (seven areas in thiscase) for the above-described allocation of the PN series as shown inFIG. 12. Therefore, 14 position vectors are allocated as shown in thedrawing. Each position vector is two-value (0, 1) data, and a 9-bitvector is used in this example. It is to be noted that establishment ofa connection between the area and the vectors is periodically repeated.

A value of each bit of these position vectors h8 to h0 is used togenerate the PN series. A circuit for generating the PN series is shownin, for example, FIG. 13. This circuit is constituted by nine flip-flopsFF8 to FF0, nine multipliers M0 to M8, and one NOR circuit. An outputfrom the NOR circuit is supplied to the flip-flop FF8, and theflip-flops FF8 to FF0 are connected in the multistage manner. Further,outputs from the respective flip-flops FF8 to FF0 are input to the NORcircuit through the multipliers M8 to M0.

The position vectors h8 to h0 are set to respective values in themultipliers M8 to M0. In these multipliers M8 to M0, there is no outputfrom a multiplier having a set value equal to 0 and an output is madefrom a multiplier having a set value equal to 1. When a predeterminedclock is input to the flip-flops FF8 to FF0, an output from a multiplierhaving a value set to 1 is fed back to the NOR circuit. A long periodicoutput called M series can be obtained in an output of the flip-flowFF0, and this is used as the PN series. It is to be noted that the PNseries may be produced by any other method.

Here, two (or three or more) types of series are allocated to one area.In the allocated PN series, the upper (higher limit) one is the PNseries corresponding to the positional data representative of one entirearea, and the lower (lower limit) one is the PN series for specifying asmall range in one area.

In the regular state, the higher limit PN series is allocated as the PNseries for the transmission wave. On the other hand, in case of thereception wave, the PN series corresponding to one entire area isdetermined as a search range so as to enable reception of the electricwave of any PN series.

Subsequently, a judgment is made as to whether an approaching vehiclethat has a possibility of a collision exists (S52). It is preferable tocarry out this judgment based on a result of calculation of crashprobability in S37, but this calculation may be executed by any othersimple operation. If this judgment is NO, the transmission/receptionseries need not be changed, and the processing is therefore terminated.

In this state, when a vehicle B exists in the vicinity of the vehicle Aand performs communication utilizing the PN series based on the samepositional data, as shown in FIG. 14(a), both vehicles effecttransmission by using the higher limit PN series in the same PN seriesand carry out reception with the area to which that PN seriescorresponds as a reception search area.

On the other hand, if the judgment at S52 is YES, the transmissionseries is shifted to an emergency series (S53). In other words,transmission is carried out using the emergency series (the lower limitPN series) which is the PN series corresponding to a narrower range asthe transmission series in the vehicle A. As shown in FIG. 14(b), thetransmission PN series from the vehicle A is shifted to the emergencyseries, but the PN series from the B vehicle is yet to be shifted to theemergency transmission series. Therefore, in regard of the receptionsearch range, the both vehicles keep to search the PN series that coversthe entire area from the beginning.

Next, a judgment is made as to whether the reception series from anothervehicle (the vehicle B in this example) is shifted to the emergencyseries (S54), and the processing waits for the shifting. The vehicle Bcan accurately grasp the communication from the vehicle A in particularsince the A vehicle transmits the data using the emergency series, a PNseries different from that of other vehicles. When the vehicle B alsodetects the possibility of a collision, the vehicle B shifts the PNseries to the emergency series.

When the reception wave from the vehicle B is shifted to the emergencyseries, the reception search range is narrowed to the emergency series(S55). That is, as shown in FIG. 14(c), the both the vehicle A and thevehicle B shift their transmission series to the emergency series andnarrow the reception search range only to the emergency range.Consequently, the both vehicles receive only the emergency series.Therefore, the vehicles A and B execute communication with the PN seriesdifferent from that of any other vehicle and are separated from othervehicles. Additionally, since the both vehicle do not search the widerPN series, they can transmit/receive much information at high speed.

When a third vehicle C detects a possibility of a collision with eitherthe vehicle A or the vehicle B, the vehicle C can break into thecommunication between the vehicles A and B.

As described above, when any other party having a possibility of acollision exists, the communication with a vehicle having a risk cantake precedence over that with other multiple vehicles to attainhigh-speed communication.

As described above, according to the system of the first and secondembodiments, the communication protocol includes at least the positionaldata. Therefore, only the data relating to a position of the user'svehicle can be received. Further, by using the emergency series, it ispossible to limit a vehicle to communicate with in case of emergency.

Third Embodiment

FIG. 15 is a block diagram showing the system structure of a vehiclecrash avoidance control apparatus according to a third embodiment of thepresent invention. A detection signal from a GPS and a sensor 112 suchas a steering or a clock is supplied to the ECU 114. The later-describedpositional data and existence probability data of the user's vehicle issupplied from the ECU 114 to a data communication section 116 andtransmitted to an other vehicle via an antenna 118. Moreover, thepositional data and the existence probability data from the othervehicle is received by the antenna 118 and supplied to the ECU 114through the data communication section 116. The ECU 114 uses therespective supplied data to calculate the later-described probability ofa collision and spatiotemporal position and recognizes the need ofavoidance of a collision.

In addition, an actuator 120 for brake or steering is connected to theECU 114. When it is determined in the ECU 114 that avoidance of acollision is necessary, the actuator 120 is driven to operate the brakeor the steering to avoid a collision with another vehicle.

As described above, in the vehicle crash avoidance control apparatusaccording to this embodiment, the avoidance control is carried out basedon the probability of a collision and a spatiotemporal position of acollision calculated by the ECU 114.

The control for avoiding a collision with another vehicle using theabove-mentioned system will now be described in detail with reference tothe attached flowcharts.

FIGS. 16 and 17 are flowcharts in which the crash avoidance controlprocessing in the user's vehicle is shown.

In the user's vehicle, the positional data of the user's vehicle isinput from the GPS 110 to the ECU 114. Further, the data representativeof a vehicular motion of the user's vehicle is inputted from the sensor112 to the ECU 114 (S110). In this example, the data representative of avehicular motion of the user's vehicle may include, for example, aturning velocity, an angle of a steering wheel, a vehicle speed, anacceleration, an estimate of driving torque, an estimate of a roadsurface friction coefficient, a road surface cant, a slope estimate, anestimated weight of a vehicle, or other information.

Subsequently, the operation for predicting the future vehicular motionis performed (S112). A sequential simulation is executed using thepositional data of the user's vehicle and the data representative of thevehicular motion of the user's vehicle to calculate position coordinatesof four corners of the vehicle from the present time to a few secondslater. For the positions of four corners of the user's vehicle, avehicle model such as a vehicular width or entire length of the user'svehicle may be used. Moreover, in place of executing the sequentialsimulation, multiple patterns of the position coordinate and theprobability distribution from the present time to a few seconds latermay be learnt in advance to specify the sequential position coordinatesfrom the input data during traveling by the neutral network.

An error may be generated in the positional data of the user's vehicledue to the state of the electric wave reception by the GPS. The dataindicative of the vehicular motion of the user's vehicle may alsoinclude a given fixed error because of an error of a detecting sensor.As a countermeasure, an error is added to the position coordinate of theuser's vehicle calculated based on the simulation. Then a higher limitvalue and a lower limit value of the position coordinate of the user'svehicle including an error are obtained.

FIG. 18 shows the position coordinates of the four corners of the user'svehicle having an error added thereto from the present time (an initialposition in FIG. 18) to a few seconds later. In this example, atrajectory A is a higher limit value of the position coordinateincluding an error, whilst a trajectory B is a lower limit value of theposition coordinate including an error. The user's vehicle exists in anyof spatiotemporal position on trajectory A or trajectory B.

Here, the probability that the user's vehicle exist in the space-timeshown in FIG. 18 is calculated. For example, a portion where thetrajectory A overlaps on the trajectory B is such a position as that theuser's vehicle is expected to positively pass, i.e., such a position asthat the probability of existence of the user's vehicle is expected tobe 100%. Further, a portion where the both trajectories A and B do notoverlap and only the trajectory A or the trajectory B exists is such aposition as that the probability of existence of the user's vehicle isexpected to be not less than 0% and not more than 100%. Moreover, aportion where the both trajectories A and B do not exist is such aposition as that the probability of existence of the user's vehicle isexpected to be 0%.

FIG. 19 is a distribution acquired by connecting an area in which theprobability of existence of the user's vehicle is 0% with an area inwhich the probability of the same is 100% obtained from FIG. 18 by astraight line. In this way, the probability of existence of the user'svehicle in the space-time from the present time to a few second latercan be calculated.

It is to be noted that the calculation in the processing of S112 maypreferably be performed in ECU 114.

As an alternative method for obtaining the existence probabilitydistribution shown in FIG. 19, a stochastic differential equation isproduced from an equation of motion of the user's vehicle, and theproduced equation is solved. A method for deriving this stochasticdifferential equation will now be explained. An x direction and a ydirection cited herein correspond to an x direction and a y direction ineach of FIGS. 18 and 19.

Forces generated in four tires from a throttle, an angle of steering,and a brake are calculated. It is assumed that a force generated in thex direction which is a force generated in the tires is determined as fxi(i=1, 4) and, in particular, fx1 and fx2 are forces generated in thefront wheels whilst fx3 and fx4 are forces generated in the rear wheels.Further, it is assumed that a force generated in the y direction whichis a force generated in the tires is determined as fyi (i=1, 4) and, inparticular, fy1 and fy2 are forces generated in the front wheels whilefy3 and fy4 are forces generated in the rear wheels. Additionally,assuming that: Vx is an X direction component of the car body velocity;Vy, a Y direction component of the car body velocity; r, a yaw anglevelocity; M, a mass of a vehicle; I, an inertia moment of a vehicle; Lf,a distance from a center of gravity to front wheels of a vehicle; Lr, adistance from a center of gravity to rear wheels of a vehicle; Df, atread of the front wheels; and Dr, a tread of the rear wheels, thefollowing three equations of motion can be obtained:

M(dVx/dt)=Σfxi+M·Vy·r  (1)

M(dVy/dt)=Σfyi+M·Vx·r  (2)

I(dr/dt)=Lf(fx1+fx2)+Lr(fx3+fx4)+2/Df(fy1+fy2)+2/Dr(fy3+fy4)  (3)

From the above equations (1), (2) and (3), the following three equationsfor deriving a slip angle β and coordinates of the center of gravity ofthe user's vehicle X and Y can be obtained:

β=tan⁻¹(Vy/Vx)  (4)

X=S{(Vx ² +Vy ²)·cos(β+Sr·dt}}dt  (5)

Y=S{(Vx ² +Vy ²)·sin(β+Sr·dt}}dt  (6)

The position coordinates of the four corners of the user's vehicle canbe derived from the coordinates of the center of gravity of the user'svehicle calculated from the above (4), (5) and (6).

The existence probability distribution shown in FIG. 19 is then obtainedby utilizing the above equations (4), (5) and (6). It is assumed thatthe position coordinate of a vehicle at a given time is determined as(b1(t), b2(t)). b1 is derived from the above expression (5); and b2 isderived from the above expression (6). It is assumed that an errorgenerated due to irregularity in the vehicle characteristics or adrive's behavior is determined as σij (i, j=x, y) and the existenceprobability distribution to be obtained is determined as u (t, x, y).With σij as a spread coefficient, the following partial differentialequation can be derived from the Kolmogorov equation:

∂u/∂t=½·Σ{{Σkiσkj)·∂² u/(∂i·∂j)}+Σ(bl·∂/∂1) where (i, k, j, l=x, y)  (7)

A first member in the partial differential equation (7) is a member thatindicates the spread and represents that inconsistency in the vehiclecharacteristics or a driver's behavior results in the extended range ofthe possible position of the vehicle with elapse of time. Further, asecond member in the equation (7) represents a change in position due tovehicular motion when there is no spread, i.e., the vehicular motionwhen there is no inconsistency in the vehicle characteristics or adriver's behavior. The equation (7) is solved by the sequentialcalculation to obtain a numeric solution of the existence probabilitydistributionμ. In this manner, the probability distribution shown inFIG. 19 can be obtained from the equation. The position coordinate ofthe four corners and the existence probability distribution of theuser's distribution can be derived by use of the equation in thismanner.

The position coordinate of the four corners of the user's vehicle fromthe present time to a few seconds later shown in FIG. 18 and the data ofthe existence probability distribution shown in FIG. 5 are transmittedfrom the antenna 18 to another vehicle through the data communicationsection 16 (S114).

On the other hand, the above-described arithmetic operation is alsoperformed in another vehicle to transmit the data representative of theposition coordinates of the four corners and the existence probabilitydistribution of another vehicle from the present time to a few secondslater.

In the user's vehicle, a judgment is then made as to whether the signalfrom another vehicle has been received (S116). If NO, it is determinedthat there is no other vehicle near the user's vehicle and the controlreturns to the processing S110. If YES, it is determined that there isanother vehicle near the user's vehicle and data representative of theposition coordinates of the four corners and the existence probabilitydistribution of another vehicle transmitted from that vehicle isreceived from the antenna 118 through the data communication section(S118).

When a signal from another vehicle is received, the arithmetic operationfor obtaining the collision probability is executed based on thereceived data representative of the position coordinates of the fourcorners and the existence probability distribution of another vehicleand the data representative of the position coordinates of the fourcorners and the existence probability distribution of the user's vehicle(S120). FIG. 20 shows the position coordinates at which the existenceprobability is 100% as a trajectory of the user's vehicle out of theposition coordinates of the four corners of the user's vehicle from thepresent time to a few seconds later illustrated in FIG. 18. Similarly, atrajectory of another vehicle is depicted. In FIG. 20, a portion wherethe trajectory of the user's vehicle overlaps on that of another vehicleis a position at which a collision can be expected in the future.

Although the position coordinates at which the existence probability is100% is a trajectory of the user's vehicle or another vehicle in FIG.20, the position coordinates at which the existence probability is above0% may be shown as the trajectory of the user's vehicle or anothervehicle. In this case, it is preferable that the probability of acollision is a product of the existence probability of the user'svehicle and that of another vehicle at a position where the trajectoryof the user's vehicle overlaps on that of another vehicle.

Also, in the processing S120, the relative velocity of the user'svehicle and another vehicle is obtained to calculate a magnitude of theimpact shock which is predicted at the time of a collision between theuser's vehicle and another vehicle. Since the magnitude of the impactshock can be expressed by, for example, a value which is proportionateto a square of the relative velocity of the user's vehicle and anothervehicle, the relative velocity may be used as a value for judgment.

Subsequently, a judgment is made as to whether or not the crashprobability is less than a given fixed value and the impact shock islarge (S122). As to threshold values for the judgment in the processingS122, it is determined that the crash probability is, for example, 95%and the relative velocity representative of the magnitude of the impactshock is 40 km/s. In a NO case, because the crash probability is low orthe magnitude of the impact shock is small, the crash avoidance controlis not positively executed and the crash avoidance control processing isterminated. It is to be noted that an appropriate avoidance control maybe directed to a driver before termination of the control in accordancewith the probability of the crash. In a YES case, since the crashprobability is high and the magnitude of the impact shock is large, thecontrol returns to the processing of S130 to perform the avoidancecontrol.

In S130, the arithmetic operation for obtaining the vehicular motionrealized when decelerating by a maximum braking force is performed(S130). For example, the vehicle positions and the relative velocity ofthe user's vehicle and another vehicle are calculated with respect tothe both a case where the user's vehicle executed the full-brakingcontrol and a case where full-braking control was not executed. Ajudgment is made as to whether the brake control is enabled by using thecalculated relative velocity (S132). For example, when another vehicleapproaches from the rear side, the relative velocity becomes a negativevalue. In this state, when the brake control is effected, that vehiclemay come into collision with another vehicle approaching from behind. Insuch a case, a driver is directed to carry out various kinds ofoperation other than the brake control in order to avert a collision(S133).

If S132 is YES, the time required for averting a collision (a collisionavoidance time) using maximum braking force is calculated (S134). Whenbrake control is executed, the crash avoidance time can be obtained froma minimum distance relative to another vehicle and the relative velocityusing the following formula:

(crash avoidance time)=(minimum distance relative to another vehiclewhen executed the brake control)/(relative velocity)

Based on this crash avoidance time, a judgment is made as to whether adriver has additional time before the crash (S136). If NO in S136, i.e.,if the driver has not additional time before the crash, the actuator 120is directed to apply the brake by the maximum braking force (S138) toterminate the avoidance control.

If YES in the processing of S136, i.e., if the driver has additionaltime before the crash, the control for averting the crash does have tobe immediately executed. As a countermeasure, taking into account roadconditions and the like, a judgment is made on to which of the user'svehicle or another vehicle the right for effecting the crash avoidanceoperation by priority (avoidance priority) is set in the future (S140).

FIG. 21 details the avoidance priority judgment in S150. At first, fromthe positional relationship between the user's vehicle and anothervehicle on the road, a judgment is made as to whether the user's vehiclecan travel by priority in accordance with road rules (S150). If NO,since another vehicle can travel by priority in accordance with roadrules, that vehicle should perform the avoidance control by priority inthe future, and the avoidance priority is set to that vehicle (S152).

If YES in S150, i.e., if the user's vehicle can run by priority inaccordance with road rules, a judgment is made as to whether the speedof the user's vehicle is higher than that of another vehicle (S154). IfNO, i.e., if the speed of another vehicle is lower than that of theuser's vehicle, since another vehicle having the lower speed can readilyexecute the crash avoidance operation, the avoidance priority is set tothat vehicle (S152).

If YES in S154, a judgment is then made as to whether there is apossibility of scrape between the user's vehicle and a third vehicleother than another vehicle in the future when the user's vehicle doesnot perform the avoidance control (S156). If NO, i.e., if there is nopossibility of the user's vehicle scraping the third vehicle, since theuser's vehicle does not have to be brought under the avoidance control,another vehicle should perform the avoidance control in the future bypriority, and the avoidance priority is set to that vehicle (S152). IfYES, i.e., if there is a possibility of the third vehicle scraping theuser's vehicle in the future unless the avoidance control is executed,the avoidance priority is set to the user's vehicle (S158).

As shown in FIG. 21, when the avoidance priority is decided by theprocessing of S140 illustrated in FIG. 17, a judgment is then made as towhether the user's vehicle have the avoidance priority (S142). Here, inexpectation that the user's vehicle has the avoidance priority andcarries out the brake control in the future, a brake controlprearrangement flag is set to ON (S144), and the control returns to theprocessing of S110. If the user's vehicle has no priority, the controldirectly returns to the processing of S110 without any change.

It may be preferable to check a failure of the actuator at the same timein the processing of S142.

In addition, when the brake control prearrangement flag is ON, it may bepreferable to derive the trajectory of the user's vehicle obtained atthe time of having performed the brake control by the user's vehiclewhen calculating the future vehicular motion in S112 after S110 and thefollowing processing in FIG. 16.

As described above, in the crash avoidance control processing accordingto this embodiment, the highly-accurate existence probability dataincluding the positional data and the positional error istransmitted/received between the user's vehicle and another vehicle bythe inter-vehicle communication to carry out the crash avoidance controlprocessing. The accurate motion information of another vehicle can betherefore obtained, thereby executing the further accurate avoidancecontrol.

Fourth Embodiment

FIG. 22 shows a block diagram of the system structure of a vehicle crashavoidance control apparatus according to a fourth embodiment of thepresent invention. In addition to the structure illustrated in FIG. 15,one additional antenna is added so that the user's vehicle is equippedwith two antennas 190 and 191. A pulse is omnidirectionally transmittedfrom the antenna 190 in unspecified directions. A pulse having the samephase with that of the antenna 190 is omnidirectionally transmitted fromthe antenna 191 in unspecified directions. Further, another vehicle isalso equipped with two antennas 193 and 194. As similar to the antennas190 and 191, pulses having the same phase are omnidirectionallytransmitted from the antennas 193 and 194 in unspecified directions.

The pulses having the same phase transmitted from the antennas 193 and194 of another vehicle are received by the antennas 190 and 191 of theuser's vehicle. A phase difference is generated in the pulses of anothervehicle received by the antennas 190 and 191 of the user's vehicle inaccordance with a distance between the user's vehicle and anothervehicle. From this phase difference, a relative distance of the user'svehicle and another vehicle can be calculated. A calculation method isdescribed below.

FIG. 23 shows a flowchart of the control processing by the vehicle crashavoidance control apparatus having the system structure illustrated inFIG. 22. Data is first input from each sensor of the user's vehicle(S160). The processing of S160 is the same with that of S110 depicted inFIG. 16.

The arithmetic operation for obtaining the future motion of the user'svehicle is then carried out (S162). In this example, although thearithmetic operation for obtaining the future motion of the user'svehicle is similar to that of S112 in FIG. 16 described above, thesimulation is performed by using only the data indicative of the motionof the user's vehicle without using the positional data of GPS in orderto calculate the position coordinates of the four corners of the user'svehicle from the present to a few seconds later and the spatiotemporalexistence probability of the user's vehicle. These position coordinatesof the four corners of the user's vehicle are not the absolutecoordinates because the positional data from the GPS is not used.

Next, a result of the arithmetic operation and a pulse signal fordetecting a phase difference are transmitted (S164). At this point, ifthe positional data of the user's vehicle from the GPS has already beenreceived, the positional data is transmitted together with the result ofthe arithmetic operation and the pulse signal for detecting a phasedifference. If no positional data from the GPS has been received, onlythe result of the arithmetic operation and the pulse signal fordetecting a phase difference are transmitted.

Subsequently, a judgment is made as to whether the pulse signal fromanother vehicle has been received (S166). If NO, the control returns tothe processing of S160. If YES, a judgment is made as to whether thedata of the user's vehicle and another vehicle includes the positionaldata from the GPS (S168).

If YES in the processing of S168, the probability of a crash withanother vehicle and the magnitude of the impact shock at the time of acollision are calculated from the positional data of GPS (S170). Here,the absolute position of another vehicle and the user's vehicle isapparent from the positional data of the GPS and, as similar to theprocessing of S120 shown in FIG. 16, the magnitude of the impact shockof a collision is calculated based on a position of a collisionpredicted from the position coordinates of the four corners and theexistence probability of the user's vehicle and another vehicle and onthe relative velocity at the time of a collision.

If a NO is decided at S168, either the user's vehicle or the othervehicle can not receive the electric wave from the GPS. In this case,the absolute position of the user's vehicle and the other vehicle cannot be recognized. In this embodiment, the relative position of theuser's vehicle and the other vehicle is obtained from a phase differenceof the pulses received by the two antennas in place of the positionaldata of GPS to calculate the crash probability and the magnitude of theimpact shock at the time of a collision (S172).

FIG. 24 shows a method for calculating the relative position of theuser's vehicle A and another vehicle B. In this embodiment, it isassumed that the antennas 190 and 191 of the vehicle A are provided withan interval L therebetween and the antennas 193 and 194 of the vehicle Bare provided with the same interval L therebetween. The pulsetransmitted from the antenna 194 of the vehicle B is received by theantennas 190 and 191 of the vehicle A with a phase differencecorresponding to a distance c. The pulse transmitted from the antenna193 of the vehicle B is received by the antennas 190 and 191 of theuser's vehicle A with a phase difference corresponding to a distance b.The pulses having the same phase transmitted from the antennas 193 and194 of the vehicle B are received by the antenna 190 of the vehicle Awith a phase difference corresponding to a distance a. In this manner,the distances a, b and c can be calculated from the phase difference inpulse of the vehicles A and B.

Here, assuming that a distance between the antenna 190 and the antenna193 is La and an angle at which the vehicle B is viewed from the vehicleA is θ (an angle between a line segment connecting the antenna 190 tothe antenna 191 and another line segment connecting the antenna 190 tothe antenna 194), they can be expressed by the following formulas:

La=L·sin(arc cos(a/1))/(tan(arc cos(c/1)−arc cos(b/a)))

θ=arc cos(c/1)

The relative distance La between the vehicles A and B and the angle θ atwhich the vehicle B is viewed from the vehicle A can be calculated inthis manner, thereby recognizing the relative position between thevehicles. When the relative position is obtained, the crash probabilitycan be calculated based on the positional data and the existenceprobability of the user's vehicle calculated in S102.

A judgment is then made as to whether the crash probability is high andas to whether the crash impact shock is large (S174), after which thecrash avoidance operation is performed if necessary.

As described above, in this embodiment, the relative position of anothervehicle calculated based on the pulses transmitted/received by theantennas mounted in the vehicle can be used to calculate the probabilityof scrape, thereby enabling the crash avoidance control.

As mentioned above, in the third and fourth embodiments, the positionaldata relating to the positions and the spatiotemporal existenceprobability data are transmitted/received between the user's vehicle andanother vehicle by the inter-vehicle communication means in the vehiclecrash avoidance control apparatus, and the spatiotemporal position atwhich a collision occurs is calculated based on these data.

Accordingly, accurate motion information of another vehicle can beobtained to carry out more accurate avoidance control.

Fifth Embodiment

FIG. 25 illustrates a block diagram of the structure according to afifth preferred embodiment of the present invention. The user's vehicle210 and other vehicles A and B perform inter-vehicle communication andtransmit/receive their traveling data.

The user's vehicle 210 is equipped with a communication antenna 212 aswell as a data communication section 214, an electronic control unit ECU216, various sensor sections 218 and an actuator section 220.

After modulating the traveling data of the user's vehicle 210, or moreconcretely, a predicted position, a predicted speed, and a predictedacceleration after a predetermined time calculated based on the currentposition, a steering angle and a speed of the user's vehicle, the datacommunication section 214 transmits the data to other vehicles throughthe antenna 212 and receives the traveling data transmitted from othervehicles so that the section 214 supplies the data to the ECU 216 afterdemodulation. The specific structure of the data communication section214 will be described later.

Specifically, the ECU 26 is a microcomputer which calculates a predictedposition, a predicted speed, and a predicted acceleration of the vehicleafter a predetermined time as described above and also evaluates thepossibility of a collision between the user's vehicle and anothervehicle based on a predicted position, a predicted speed and a predictedacceleration of another vehicle which are received from that vehicle.When it is determined as a result of this evaluation that there is apossibility of a collision, a priority of the user's vehicle and anothervehicle is further determined, and a control signal is supplied to theactuator section 220 based on the priority to execute the avoidancetraveling of the user's vehicle. When executing the avoidance traveling,the basic principle is not to perform the avoidance operation such asdeceleration without variation if there is a possibility of collision,but rather to effect the avoidance operation of the user's vehicle ifcomparison of the priority of the user's vehicle with that of anothervehicle reveals that the priority of the user's vehicle is low or not toeffect the avoidance operation if the priority of the user's vehicle ishigh (or to restrictively perform the avoidance operation (for example,simply sounding a horn) even if that operation is carried out andanother vehicle takes charge of the primary avoidance operation).

The sensor section 218 includes a GPS, a steering angle sensor, and aspeed sensor and supplies the detected current position, the steeringangle and the speed of the vehicle to the ECU 216.

The actuator section 220 comprises a brake actuator, a steeringactuator, a buzzer, and other such components and effects the avoidanceoperation such as deceleration by braking, steering, or prompting adriver to perform these operations in accordance with the control signalfrom the ECU 216.

FIG. 26 illustrates a flowchart of the entire processing of thisembodiment. First, a signal is input from the sensor section 218 to theECU 216 (S201). Specifically, the input signal includes the positionaldata by the GPS, the steering angle and the vehicle speed. A relativeposition with respect to another vehicle obtained by a radar mounted inthe vehicle, a yaw rate, a driving torque estimate, a road surface μestimate, a road surface cant, a slope estimate, an estimated weight ofa vehicle, or the like may also be input. Upon obtaining this data, theECU 216 calculates the traveling data of the user's vehicle (S202). Apredicted position, a predicted speed, and a predicted acceleration ofthe user's vehicle are calculated after a predetermined time, typically,a few seconds. In an example using predicted position, the ECU 216effects the sequential simulation from the four-wheeled vehicle modeland calculates the position coordinates of the four corners inspace-time (a space axis and a time axis) from the present time to a fewseconds later. A positional error due to the state of the electric waveof the GPS and the positional error due to irregularity in the vehicularcharacteristics are added to the position coordinates. Taking intoaccount error, the predicted position can be expressed in the form ofthe probability ( existence probability distribution).

The calculated traveling data is then periodically transmitted to theother vehicle (S203). As a transmission procedure, the traveling dataobtained by the arithmetic operation is divided in accordance with thetime and the positional data. The example is as shown in Table 5.

TABLE 5 Probability of Time Position Existence 1.01 (1012.6, 104.6,15.2) 1.0  2.21 (1010.3, 105.2, 15.2) 0.95 3.35 (1008.3, 107.2, 15.2)0.88

The time and the positional data are rounded off to appropriate units(the least significant bit LSB is rounded off) and combined to create aseries of sequence of numbers. The produced sequence of numbers israndomized by a predetermined encoding process. For example, the timeand the position at the time 1.01 in the Table 5 are converted asfollows:

1.0, 1013, 0105, 15

→101013010515

→730184621803869

The thus-created sequences of numbers are used as random numbers fordetermining the PN series for the spread spectrum communication or thepattern of the hopping frequency.

It is to be noted that only the current position coordinates of theuser's vehicle are used to produce the PN series or the hoppingfrequency. However, since a plurality of vehicles may possibly exist inthe different LSBs when rounding off the position coordinates, asequence of numbers corresponding to a vehicle ID is added to thecounterpart of the positional information in order to preventinterference so that the PN series or the pattern of the hoppingfrequency is determined. For example, if the ID of the user's vehicle is0323 and its current position is (1012.0, 1411.0, 15.0), the followingsequences of numbers can be obtained:

0323, 1012.0, 1411.0, 15.0

→40.231012141115

→846120973956829

The actual transmission information includes an accurate time, thepositional information, and the existence probability at that position,and these are converted into pulses to be carried in digitalcommunication.

FIG. 28 illustrates a transmission structure of the data communicationsection 214 in an example employing spread spectrum communication. Thechip time (the wavelength) of the carrier wave having a frequency whichis much higher than that of the pulse transmitted by a primarymodulating section 214 a is changed and the modulation signal and the PNseries generated in a PN series generator 214 c are multiplied by amultiplier 214 b so that a result of multiplication is transmitted froman antenna 212 through a band-pass filter 214 d. It is to be noted thatthe frequency is subjected to hopping to create a carrier wave inaccordance with sequences of numbers in case of the frequency hopping.Further, the transmission data may include the current position or thespeed of the user's vehicle.

After transmitting the traveling data of the user's vehicle to anothervehicle, the traveling data transmitted from the other vehicle isreceived (S204). When receiving, the electric wave transmitted by theuser's vehicle is filtered or temporally removed, and the spatiotemporalproximate data is added to the data obtained by rounding off the timeand the positional data of the user's vehicle generated at the time oftransmission according to need to produce the random numbers as similarto transmission. For example, as the data for transmission, combinationand encoding of the time 1.0 and the position (1013, 0105, 15) canobtain a sequence of numbers 730184621803869; the time 1.0 and theposition (1014, 0105, 15) which are the spatiotemporal proximate dataare used to produce a sequence of numbers 530144621893867; and the time1.5 and the position (1013, 0105, 15) are used to generate a sequence ofnumbers 730884621893865. The produced sequence of numbers are used asrandom numbers for determining the PN series for the spread spectrum orthe pattern of the hopping frequency and received.

FIG. 29 shows the reception structure of the data communication section214 in an example of spread spectrum communication. The signal receivedby the antenna 212 is transmitted through a band-pass filter 214 e, andthe reception signal and the sequence of numbers are multiplied by amultiplier 214 f to release the PN so that the processed signal isdemodulated by a demodulator 214 h. When the PN series is generate byusing the vehicle ID at the time of transmission, it is needless to saythat the vehicle ID is similarly used to create the PN series inreception.

Upon receiving the traveling data of the other vehicle (YES in S205) asmentioned above, the probability of a collision or scrape involving theuser's vehicle and the other vehicle whose data has been received in thespace-time and the magnitude of impact shock of a collision (scrape) arecalculated (S206).

FIG. 33 illustrate an example of the spatiotemporal positionalrelationship between the user's vehicle and the other vehicle whose datahas been received. In the drawing, the coordinates are space coordinatesX and Y and the time coordinate t. The drawing shows a trajectory of apredicted position in the space-time of the user's vehicle and atrajectory of a predicted position in the space-time of another vehicle.An error is included in each predicted position as described above andthe existence probability is provided for each position. If thepredicted positions of the user's vehicle and another vehicle overlapeach other at a portion corresponding to the existence probability 100%,the crash probability is 100%. If they overlap each other at a portioncorresponding to the existence probability 0% to 100%, a maximum valueof a product of the existence probabilities at the overlap portionbecomes the crash probability. For example, a portion where theexistence probability of the user's vehicle is 60% overlaps on a portionwhere the existence probability of another vehicle is 50%, theprobability of a crash becomes 60%×50%=30%.

Meanwhile, since the magnitude of impact shock of a collision isproportionate to the motion energy, the relative velocity of the user'svehicle and another vehicle at a position where a finite (not 0) crashprobability is first generated is calculated, and a square of anabsolute value of the obtained relative velocity is multiplied by apredetermined constant to derive the magnitude of the impact shock.

After evaluating the probability of collision and the magnitude of theimpact shock, the ECU 216 makes a judgment as to whether the probabilityof collision is higher than a predetermined value and the magnitude ofimpact shock is greater than a predetermined value (S207). If theprobability of collision is determined to be high and the magnitude ofimpact shock is large, it is decided that the avoidance operation isnecessary to execute a predetermined optimum avoidance controlarithmetic operation (S208).

This optimum avoidance control arithmetic operation judges on whetherthe deceleration control is appropriate and calculates a margin for theavoidance, and its detailed flowchart is shown in FIG. 30.

In FIG. 30, the vehicular motion (a predicted position, a predictedacceleration and a predicted acceleration) on the assumption that theuser's vehicle has decelerated by the maximum braking force iscalculated (S221). Then, the calculated amount of vehicular motion isused to again evaluate the probability of collision with another vehicleand the magnitude of impact shock of collision, and a judgment is madeas to whether the magnitude of the impact shock on the assumption thatthe user's vehicle has decelerated by the maximum braking force(assumption that another vehicular runs without deceleration aspredicted) is lower than the magnitude of the impact shock in case of nodeceleration by the maximum braking force (the magnitude of the impactshock calculated in S206) (S222). If the magnitude of the impact shockis lowered (including the case of no crash), it is determined that thebrake control is effective to set the brake control to the enabled state(for example, the brake control flag B is set to 1: S223). Meanwhile, ifthe magnitude of the impact shock is not lowered (if the magnitude isunchanged or becomes large due to braking), it is determined that thebrake control is not effective to set the brake control to the disabledstate (the flag B is set to 0) (S224). The margin for avoidance iscalculated based on the minimum distance relative to another vehicle atthe time of avoidance (the minimum distance relative to another vehiclewhen the existence probabilities are all 100% with errors in thepredicted positions of the user's vehicle and another vehicle includedin the calculation) and the relative velocity of the user's vehicle andanother vehicle (the current relative velocity) (S225). Specifically,the margin for avoidance is calculated by the following expression:

Margin for Avoidance=Minimum Distance/Relative Velocity

This equation is based on the fact that the larger the minimum distanceis the greater the margin is and the both vehicles approaches each otherslowly and thus have the margin as the relative velocity of the user'svehicle and another vehicle is small. Incidentally, since the steeringoperation is effected to avert a collision when the brake control is indisabled state, the margin for avoidance can be calculated with theminimum distance obtained when the appropriate steering operation iscarried out.

Again referring to FIG. 27, after executing the optimum avoidancecontrol arithmetic operation as mentioned above, a judgment is made asto whether a driver has additional time before the avoidance by usingthe calculated margin for avoidance (S209). If the margin for avoidanceis not less than a predetermined value and the driver has additionaltime to avoid a collision (NO in S209), the traffic priority of theuser's vehicle and another vehicle is examined in order to performfurther effective avoidance (S211).

FIG. 31 illustrates the detail of the processing in S211. Cruising lanesand roads of the user's vehicle and another vehicle are first specifiedbased on map data stored in a memory (not shown in FIG. 25: the map dataof a navigation system can be used), the detected position of the user'svehicle and the received position of another vehicle to detect apriority relationship between the user's vehicle and another vehicle inaccordance with road rules (S231). A judgment is made as to whether theuser's vehicle takes priority (S232) and, if the user's vehicle does nottake priority, a priority flag for another vehicle is set (for example,a flag P is set to 1: S230). If the user's vehicle takes priority inaccordance with road rules, the current traveling speeds of the user'svehicle and another vehicle are compared with each other (S233). If aresult of comparison reveals that the speed of another vehicle ishigher, the priority flag for another vehicle is set (S239). Thepriority is given to the vehicle having the higher speed because it canbe considered that execution of the avoidance operation by the vehiclehaving the higher speed is generally difficult and largely affects thetraffic flow.

On the other hand, if the user's vehicle have the speed higher than thatof another vehicle, a judgment is then made as to whether there is apossibility of collision with a third vehicle (any vehicle other thananother vehicle which is determined to have a possibility of a collisionin S207) by the avoidance control of the user's vehicle (S236). Thisjudgment is enabled by, for example, existence or absence of a vehiclefollowing the user's vehicle and existence or absence of any vehicletraveling in a lane adjacent to that of the user's vehicle (existence ofthese vehicles can be detected by the inter-vehicle communication or aradar apparatus mounted in the user's vehicle); the priority is given toanother vehicle if there is no possibility of a collision with the thirdvehicle (S238); and the same is given to the user's vehicle if there isa possibility of collision with the third vehicle (S237). The user'svehicle executes the avoidance operation if “another vehicle takespriority”, whilst the user's vehicle does not execute the avoidanceoperation if “the user's vehicle takes priority.”

Again referring to FIG. 27, upon completion of examination of thetraffic priority, a judgment is made as to whether the user's vehicletakes no priority (another vehicle takes priority) and the actuatorsection 20 malfunctions (S212). If the user's vehicle takes priority andthe actuator section normally operates, the user's vehicle must performthe avoidance operation, and hence the content of the avoidance controlis included in the next vehicular motion arithmetic operation to betransmitted to another vehicle (S213). Since this enables anothervehicle to receive the data representing that the user's vehicle effectsthe avoidance operation in the next reception, another vehicle does notcarry out the avoidance operation. Incidentally, although the ECU 216 ofanother vehicle individually makes the similar judgment to decide thatthat vehicle takes priority, that vehicle decides not to execute theavoidance operation upon receiving the data indicating that the otherparty's vehicle effects the avoidance control and determines that thepriority is assigned to that vehicle rather than the other party'svehicle. However, when the data indicating that the other party'svehicle carries out the avoidance operation is not received, thatvehicle executes the avoidance operation in terms of the fail safe.After the user's vehicle transmits the data representing that the user'svehicle executes the avoidance operation to another vehicle, when it isdetermined that there is no additional time to avert a collision in thenext judging processing (YES in S209), the ECU 216 of the user's vehicleperforms a predetermined avoidance control (S210).

On the other hand, if YES in S209, if there is no additional time toavert a collision, the avoidance control is immediately carried out(S210).

FIG. 32 shows the detailed processing in S210. A judgment is made as towhether the brake control is enabled by checking a value of a brakecontrol flag B (S251). When the brake control is enabled, the brakingpressure is increased for deceleration so as to operate the brakeactuator by the maximum control force (S252). This prevents a collisionwith another vehicle (or suppresses the impact shock of a collision).Further, when the brake control is disabled, the brake actuator controlis terminated to reduce the braking pressure (S253). A driver is thendirected to carry out the steering operation and the like (S404). Adirection of steering is a direction for lowering the probability of acollision obtained in S206 and the impact shock.

As described above, in this embodiment, the possibility of a collisionbetween the user's vehicle and another vehicle is evaluated, and neitherthe user's vehicle nor the other vehicle perform the avoidanceoperation, even when there is a possibility of a collision but eithercarries out the avoidance operation in accordance with the priority ofthe user's vehicle and another vehicle, thereby effectively averting acollision without producing a possibility of another collision with athird vehicle being caused by the avoidance operation.

Although in the foregoing embodiment an example wherein the priority ofthe user's vehicle and another vehicle is judged and one having nopriority performs the avoidance operation were described, it is alsopossible to evaluate the priority in other terms such as, for example,percentage (the priority of the user's vehicle is 40% while that ofanother vehicle is 60%) and make a decision on a proportion of theavoidance operation in accordance with this percentage (a decelerationof the user's vehicle is 60% of a maximum deceleration and adeceleration of another vehicle is 40% of a maximum deceleration). Thatis, it is possible to share the avoidance operation by the both theuser's vehicle and another vehicle in accordance with priority ratherthan perform the avoidance control by either of them.

FIG. 34 shows a typical example of the positional relationship betweenvehicles A and B that have a possibility of a collision. The vehicle Atravels on a privileged road while vehicle B is entering the privilegedroad from a non-privileged road. When it is decided that there is apossibility of a collision from the positional relationship and thetraveling speeds of the two vehicles, both vehicles A and B generate awarning for their drivers and further perform the avoidance operation,such as deceleration by applying the brake.

However, since the vehicle A travels on the privileged road, the vehicleA keeps running and only the vehicle B should carry out the avoidanceoperation according the rules of the road, though execution of theavoidance operation such as deceleration by the vehicle A as well as thevehicle B can avert a collision between the vehicles A and B. Howeverthis results in such a problem as that a distance between the vehicle Aand a vehicle C following the vehicle A is rapidly reduced (a driver ofthe vehicle C considers that the vehicle A does not decelerate becausethe vehicle A travels on the privileged road, and the driver of thevehicle C keeps traveling).

According to the fifth embodiment, it is possible to solve such aproblem and effectively avert a collision while suppressing affection onthe traffic flow when there is a possibility of a collision between theuser's vehicle and another vehicle.

What is claimed is:
 1. An inter-vehicle communication apparatus for performing communication between vehicles, comprising: a variable communication pattern determining section for determining a modulated communication signal based on positional data associated with a position of a first vehicle; and a transmitting section for transmitting information to a second vehicle using the determined communication pattern.
 2. An apparatus as set forth in claim 1, wherein said positional data associated with a position of the first vehicle is data regarding the present position and a projected future position of the first vehicle.
 3. An apparatus as set forth in claim 2, wherein said communication pattern determining section determines a modulated communication signal utilizing time data in addition to the positional data.
 4. An apparatus as set forth in claim 1, wherein said modulated communication signal is a spread pattern for spread spectrum.
 5. An inter-vehicle communication apparatus for performing communication between vehicles, comprising: a variable communication pattern determining section for determining a modulated communication signal based on positional data associated with a position of a first vehicle; and a receiving section for receiving information transmitted from a second vehicle using the determined modulated communication signal.
 6. An apparatus as set forth in claim 5, wherein said positional data associated with a position of the first vehicle is data regarding the present position and a projected future position of the first vehicle.
 7. An apparatus as set forth in claim 6, wherein said communication pattern determining section determines a modulated communication signal utilizing time data in addition to the positional data.
 8. An apparatus as set forth in claim 5, wherein said modulated communication signal is a spread pattern for spread spectrum.
 9. An apparatus as set forth in claim 5, wherein the communication pattern determining section determines a modulated communication signal based on positional data in a predetermined search range associated with a position of the first vehicle.
 10. An apparatus as set forth in claim 9, further comprising an approaching state determining section for determining an approaching state with respect to the second vehicle, said section varying said search range in accordance with the determined approaching state.
 11. An apparatus as set forth in claim 10, wherein said search range is narrowed when said approaching state determining section determines the approaching state to be within a predetermined range. 